1. Field of Invention
The present invention relates generally to attitude determination systems, and more particularly, to an attitude determination method and system using a single directionally steered antenna and Global Navigation Satellite Systems to determine the attitude of a platform vehicle.
2. Background of the Invention
An attitude determination system is used to estimate the attitude of a platform vehicle, such as a satellite, an aircraft or a ground vehicle. Typically, the attitude determination system references a platform vehicle coordinate system relative to a known reference object in space, such as the earth, the sun satellites, stars or planets, to determine the orientation of the platform relative to a second coordinate system in which in the direction to the object is known (e.g., antenna boresight). The object's known location could be in either inertial or moving reference frame coordinates. To estimate the platform's attitude in the inertial frame, the reference object location or direction in the inertial frame is used.
Conventional methods for estimating the attitude of a platform vehicle have drawbacks. One such method uses an optical payload pointing system that utilizes stars as inertial references. This method is undesirable because optical systems are expensive and require processing to generate the attitude.
Another method utilizes a Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) receiver system and electro-optical sensors to make angular direction measurements to the GPS/GNSS satellites in order to provide 3-axis attitude estimates. This method is undesirable because optical systems are expensive and require processing to generate the attitude.
Yet another method utilizes phase difference information of a separated multi-patch antenna system. By measuring differential phase between two antennas, the platform vehicle attitude can be estimated. This method requires several multi-patch antennas and large antenna baselines for high precision making the system bulky and heavy. This method also suffers with cycle ambiguity resolution issues where the number of wavelengths between a given pair of antennas needs to be correctly resolved first before the attitude determination processing can start.
In view of the above, what is needed is a cost-effective attitude determination system to determine the attitude of a platform vehicle.